Diesel engines in certain motor vehicles often use a starting aid, particularly when engine starting is attempted in cold weather. The starting aid is employed until sufficient heat has been developed in the combustion chambers for assured combustion of injected diesel fuel by compression ignition. In the absence of using a starting aid during a cold start, in-cylinder combustion may be incomplete or not occur at all, leading to increased hydrocarbon tailpipe emissions in the engine exhaust if the engine can be started and continues running.
Known cold start aids include ether injection, block heating, and glow plugs. Glow plugs are electrically energized to heat the combustion chambers to aid combustion of injected diesel fuel. The glow plugs may continue to be energized during initial running of the engine until desired combustion chamber temperature has been reached.
A glow plug starting aid system typically has one or more glow plugs associated with each combustion chamber, and some form of control or control system that controls the delivery of electric current to the glow plugs from the vehicle battery or battery bank. The control may comprise one or more switching devices, such as relays or solid-state power switches, through which battery current is conducted to the glow plugs.
When a cold engine is to be started, the one or more switching devices are turned on to connect the glow plugs to the battery, with the electric current acting to heat the glow plugs which in turn heat the combustion chambers. The engine is thereafter cranked until it starts and begins running under its own power.
At starting and initial running of a cold diesel engine, noticeably more HC is generated in the exhaust than later on. When an engine has a DPF in its exhaust system, the DPF is effective to trap significant amounts of DPM, keeping the trapped matter from entering the atmosphere. The HC that is created as a result of incomplete combustion in a cold combustion chamber can collect on surfaces of a DPF. A consequence of this is that the DPF may require more frequent regeneration.
Certain government regulations applicable to diesel engines mandate that an ineffective glow plug be disclosed, such as by illuminating a lamp on an instrument panel. The ineffectiveness may occur for any of several reasons. The glow plug itself may malfunction. A switching device through which electricity is delivered to a glow plug may not be functioning properly. There may a fault in the glow plug control and/or associated wiring.
While the expectation from having a fault indicator like an instrument panel lamp is that corrective action will be promptly undertaken by the vehicle operator, corrective action may be delayed.